change event not triggering in extjs4.1 using refs in controller

change event not triggering in extjs4.1 using refs in controller.I have implemented following code .I have used combo box id cmbMarketRegion.can anybody correct me.If there is anything missing let me know

I am using Sencha architect to create a ref to one of my grid on the view. The definition of your ref is slightly different. Its missing a selector. Sencha Architect creates a ref in this way by default.